Propylene/ethylene/1-hexene terpolymers are already known in the art for the production of pipes. For example WO2006/002778 relates to a pipe system comprising a terpolymer of propylene/ethylene and alpha olefin wherein the ethylene content is from 0 to 9% by mol, preferably from 1 to 7% by mol and the 1-hexene content ranges from 0.2 to 5% wt.
When small diameter pipes are needed it is important to have limited wall thickness of the pipe. This allows to obtain pipes containing less material and above all to improve the efficiency of the pipe in terms of feed due to the higher internal diameter. However when the wall thickness become small the pipe could become brittle, thus it is necessary to use a material having high impact resistance, especially at low temperature.
The applicant found that it is possible to select from these ranges a composition having improved properties in particular improved impact properties to be used for small diameter pipes.